1. Field of the Invention
The present invention first of all relates to a miniature electrical drive, in particular a rotating-field drive with permanent magnet excitation, having a stator which contains a laminated iron magnetic return path, in the form of a soft-magnetic return path element which cylindrically surrounds the stator and has a multiplicity of sheet-metal laminates which are in the form of annular disks and are arranged in layers to form a cylindrical laminated core.
The invention also relates to a soft-magnetic return path element for a miniature drive such as this, comprising a multiplicity of sheet-metal laminates which are in the form of annular disks and are arranged in layers to form a cylindrical laminated core.
Finally, the invention also relates to a method for production of a magnetic return path element such as this.
2. Description of the Prior Art
German utility model DE 90 10 318 U1 describes a miniature electric motor and an associated magnetic return path cylinder of this generic type. In this as half segments and joined together to form a laminated core, thus creating two cylindrical half-shells, which are then connected in an interlocking manner to one another to form the overall magnetic return path cylinder. The individual sheet-metal laminates are integrally connected to one another by being provided with a specific lacquer layer. In order to reduce the laminated cores, the sheet-metal laminates are then heated and are integrally connected to one another via the melting lacquer. The sheet-metal laminates may, however, also be integrally connected by means of an axial weld bead. The laminated magnetic return path cylinder formed in this way is mounted on the stator by force-fitting bracing of two housing halves of an outer motor housing. The production of this known drive and of the magnetic return path element is quite complex and, from the modern point of view, the process is not adequately reliable. Furthermore, quite high eddy-current losses occur because of the large-area electrical connection between the laminated core and the motor housing.
DE 60028427 T2 discloses an assembly method for assembly of a stator of an electric motor, in which the laminated core, which is composed of sheet-metal laminates, is fixed axially within the supporting sleeve by means of end disks which are wedged in the inner wall of the supporting sleeve. With this method, there is a risk that the end disks can tilt, as a result of which the laminated core is not fixed exactly. Furthermore, high eddy-current losses occur because of the large-area contact between the laminated core and the supporting sleeve.
DE 42 24 628 A1 likewise describes a miniature electric motor, although this does not have a laminated magnetic return path element. In fact, a pole housing is composed of a cylindrically shaped, magnetically permeable metal sheet, with the pole housing being closely surrounded by an additional magnetic return path ring, likewise composed of magnetically permeable metal sheet, in order to enlarge the magnetic return path cross section. The magnetic return path element is therefore composed of two coaxial cylindrical metal sheets. The other magnetic return path ring is held axially without any play on the inner pole housing since the magnetic return path ring has cut-free lugs in two areas which axially overhang the pole housing, which lugs are bent around radially inwards once the magnetic return path ring has been pushed axially onto the pole housing, so that they clasp the end faces of the pole housing.
EP 1 501 170 A1 describes an electrical machine with a particular type of stator mounting. The electrical machine comprises a housing, a stator and a rotor. The housing has at least one area which projects inwards, in order to clamp the entire stator in the interior of the housing. This document therefore does not relate to the holding of sheet-metal laminates which are in the form of annular disks and are arranged in layers to form a cylindrical laminated core, but in fact the entire, previously assembled, stator is mounted within a housing without adhesive bonding. The document discloses nothing relating to the initial assembly of the stator with sheet-metal laminates. It can be assumed that the stator laminates are adhesively bonded to one another in the previously normal manner, for which purpose so-called stove enamel is normally used. According to the teaching of this document, only the entire stator is mounted in the outer housing, by clamping and without adhesive bonding, in this way.
A corresponding situation also quite obviously applies to the publication JP 05-199695 A.
US 2003/0098628 A1 describes an electric motor in which a stator core is composed of a plurality of parts via swaged joints.
The further publication US 2005/0269895 A1 describes a brushless DC motor, in which a stator core and a stator winding are jointly encapsulated with resin in order to form a stator subassembly. This encapsulated stator is then pushed into a cylindrical yoke.
A further motor is described in DE 690 04 513 T2 and EP 0 410 933 B1. In this case, the aim is for a stator to be surrounded by a tubular sleeve composed of insulating material, for example synthetic, thermally shrinking polyester film, or an adhesive tape wrapping.
U.S. Pat. No. 2,151,561 A describes an electrical machine in which a laminated core is held in a sleeve. The core is inserted into the interior of the sleeve by introducing the laminates into the sleeve, as a stack. They are then intended to be twisted relative to one another, effectively in the form of a bayonet connection. In one specific relative rotation position, the aim is then to produce a latching connection although there is in any case a radial joint gap between the laminated core and the sleeve in this position, because the sleeve has a cylindrical shape after latching.
Finally, the document U.S. Pat. No. 1,816,859 discloses laminates being connected by means of axial weld lines to form a core. The entire core is then turned over cylindrically, and forced into radial projections on a frame.